1. Field of the Invention
The present invention relates to a single-phase induction motor, and more particularly, to a single-phase induction motor capable of decreasing a driving torque thereof and varying a rotation speed of an induction cage rotor.
2. Description of the Conventional Art
Generally, a motor is a device for converting an electric energy into a mechanical energy, and is divided into a DC motor and an AC motor according to a used power. The DC motor includes an induction motor, a synchronous motor, a commutator motor, etc.
The induction motor has a structure that a permanent magnet rotor is free-rotatably installed at an air gap between a stator and an induction cage rotor. When the permanent magnet rotor is rotated with a synchronous speed by a rotation magnetic field of the stator, the induction cage rotor is rotated by a strong magnetic flux generated from the permanent magnet rotor.
FIG. 1 is a frontal view showing a single-phase induction motor in accordance with the conventional art, FIG. 2 is a perspective view showing a permanent magnet rotor and an induction cage rotor in the single-phase induction motor in accordance with the conventional art, and FIG. 3 is a longitudinal section view showing the permanent magnet rotor and the induction cage rotor in the single-phase induction motor in accordance with the conventional art.
As shown, the conventional single-phase induction motor 10 comprises a stator 11 fixed to inside of a casing (not shown), an induction cage rotor 13 rotatably installed in a receiving groove 12 of the stator 11, a permanent magnet rotor 14 free-rotatably installed between the stator 11 and the induction cage rotor 13, and a shaft 15 fixed to the center of the induction cage rotor 13.
A coil winding portion 17 on which a stator coil 16 is wound so that the stator 11 can have an N polarity or an S polarity is formed at one side of the stator 11.
The induction cage rotor 13 is provided with a shaft hole 13a for fixing the shaft 15 at the center thereof, and a plurality of conductor holes 13b are formed at the outer peripheral portion thereof in a circumferential direction with the same interval. Each conductor hole 13b is provided with a conductor bar 13c, and an end ring 13d is formed at an end of the conductor bar 13c. 
The permanent magnet rotor 14 includes a frame 14a for rotatably coupling the shaft 15 to the center thereof, and a permanent magnet 14b coupled to the end of the frame 14a in a circumferential direction and freely-rotated by the rotation magnetic field of the stator 11 for rotating the induction cage rotor 13. The frame 14a is provided with a shaft bearing 15a at the center thereof.
An operation of the conventional single-phase induction motor will be explained as follows.
When power is supplied to the stator coil 16, the stator coil 16 generates a rotation magnetic field.
By the rotation magnetic field of the stator coil 16, the stator 11 generates a rotation magnetic field.
The rotation magnetic field of the stator 11 is transmitted to the permanent magnet rotor 14, and thereby the permanent magnet rotor 14 is freely rotated with a synchronous speed. The permanent magnet rotor 14 generates a rotation magnetic field having a strong flux and the induction cage rotor 13 is rotated by the generated rotation magnetic field.
However, the conventional single-phase induction motor has to be operated in a constant consumption power, thereby degrading a driving performance and not varying a speed of the induction cage rotor.